Schizophrenia is a chronic psychiatric disorder generally preceded by a so-called prodromal phase, which is characterized by attenuated psychotic symptoms. Advances in clinical research have enabled prospective identification of those individuals who are at clinical high risk (CHR) for psychosis, with the power to predict psychosis onset within the near future. Changes in several brain neurochemical systems and molecular mechanisms are implicated in the pathophysiology of schizophrenia and the psychosis spectrum, including the dopaminergic, γ-aminobutyric acid (GABA)-ergic, glutamatergic, endocannabinoid, and immunologic (i.e. glial activation) system and other promising future directions such as synaptic density, which are possible to quantify in vivo using positron emission tomography (PET). This paper aims to review in vivo PET studies in the mentioned systems in the early course of psychosis (i.e. CHR and first-episode psychosis (FEP)). The results of reviewed studies are promising; however, the current understanding of the underlying pathology of psychosis is still limited. Importantly, promising efforts involve the development of novel PET radiotracers targeting systems with growing interest in schizophrenia, like the nociceptive system and synaptic density.
Keywords: Positron emission tomography; at risk mental state; clinical high risk; first episode; schizophrenia; ultra-high risk.